The present invention relates to a lamp control circuit for selectively controlling the power supply to a plurality of lamps used as the light source of an endoscope system.
Endoscope system lighting is indispensable to endoscopic diagnosis. If a light source of the endoscope system comprises a single lamp, the endoscopic diagnosis must be interrupted upon lamp breakdown. To avoid this, two lamps, for example, may be arranged within the light supply unit of an endoscope system. A switch is arranged to switch the lamps. The switch is operated to select one of the lamps at the beginning of endoscopic diagnosis. Alternatively, the switch may be operated to select the second lamp when the first lamp is burnt out.
Halogen lamps are suitable for use as the light source of an endoscope system, since they emit light rays of high intensity. However, halogen lamps tend to be burnt out upon an abrupt increase in power. For example, when power is abruptly supplied to the halogen lamp, upon the turning on of the power switch, the filament of the halogen lamp tends to be disconnected, even if the power supplied is rated power.
In the conventional light supply unit of the endoscope system, a soft starter circuit, operated upon initiation of power supply, is used to prevent the disconnection (or burning out) of a halogen lamp. For this reason, when the first lamp is switched to the second lamp, without turning off the power supply, the second lamp can be turned on with only low precision, thus degrading the reliability of the light supply unit.